Carboxylic-acid functional polyurethane polymers and their use in magnetic recording media

ABSTRACT

The invention provides novel polyurethanes which can be used in magnetic media binders applications. The polyurethanes comprise multidentate chelating functional groups pendant from the polymer backbone, which groups are produced by esterification of backbone hydroxyl moieties with cyclic dicarboxylic acid anhydrides which also bear an additional polar functional group such as those selected from the group consisting of --H, --OH, --COOM, --SO 3  M, --SH, --CH 2  COOM, --SCH 2  COOM, --P(═O)(OM) 2 , --OP(═O)(OM) 2 , and the like. Examples of anhydrides useful in preparation of the polyurethanes include anhydrides of citric acid, mercaptosuccinic acid, dimercaptosuccinic acid and nitrilotriacetic acid. The polyurethanes, which are optionally radiation curable, show high affinity for magnetic pigments, and blends of the polyurethanes with vinyl resins afford excellent binders for magnetic recording media.

This is a division of application Ser. No. 08/054,511 filed Apr. 27,1993, issued as U.S. Pat. No. 5,498,685, Mar. 12, 1996.

FIELD OF THE INVENTION

This invention relates to polyurethane polymers having multidentatechelating functional groups comprising a carboxylic acid group and atleast one additional polar functional group adjacent thereto pendantfrom the polyurethane polymer backbone. The invention also relates tothe use of such polymers and their blends in magnetic recording media.

BACKGROUND OF THE INVENTION

Magnetic recording media generally include a binder dispersion layercomprising a binder and a pigment overlying a substrate, wherein thepigment is dispersed within the binder. Typically, the pigment is amagnetizable pigment comprising small, magnetizable particles. In someinstances, the medium may be in the form of a composite having bothback-coat and front-coat binder dispersion layers, although the pigmentin the back-coat may or may not be a magnetizable pigment.

It has become desirable to have as high a loading of magnetizablepigment in the magnetic recording media as is reasonably possible. It isoften preferred to have a binder dispersion comprising from about 70% to85% by weight magnetizable pigment relative to the binder with as manymagnetizable particles per unit area or unit volume as possible. It isalso preferred to have a binder dispersion in which the magnetizablepigment comprises a plurality of small particles having a relativelyhigh specific surface area. Higher pigment loading has the potential toprovide high density magnetic recording media capable of storing moreinformation.

Problems, however, remain in the art concerning magnetic recording mediahaving a relatively high loading of magnetizable pigment. To begin with,magnetizable pigments tend to agglomerate, and they are difficult toproperly and fully disperse within the binder. Wetting agents, ordispersants, are often employed to facilitate such dispersion. Forhigher pigment loading, i.e., the use of greater amounts by weight andnumber of magnetizable particles, greater amounts of such dispersantsare required, which is not always desirable.

There are a number of reasons for using as little dispersant aspossible. Dispersants tend to soften binder systems, decrease theirtoughness, and adversely affect their cure. Binders without dispersantscan be more readily and reproducibly prepared. Further, excessdispersant may bloom from a cured binder system over time, leading tocontamination of a recording head or the like, causing a change in thephysical or chemical characteristics of the media.

To help alleviate these problems with added dispersants, bindercompositions having internal (chemically bound) dispersants have beendeveloped. Such compositions comprise polymers with functional moietiespendant from the polymer backbone that help disperse the magnetizablepigment. As a result of using these compositions, less dispersant or, insome instances, no dispersant is needed for dispersion of magneticpigment in the binder. However, in spite of these improvements, a higherdegree of pigment-polymer interaction is desired, particularly in thecase of pigments exhibiting small particle size, such as barium ferrite.

Recently, sulfonated hydroxy-functional polyurethane-containing bindersystems have been described which exhibit excellent pigment loading andmagnetic orientation (U.S. Pat. Nos. 5,071,578 and 5,085,941, bothassigned to 3M, both incorporated by reference herein). However, thesesulfonated polyurethane binder systems are less effective in dispersingbarium ferrite (BaFe) pigments, a class of pigments of increasinglyimportant commercial consideration.

Polyurethane magnetic binder polymers containing isolated carboxylicacid groups which do not have additional polar functional groupsassociated therewith (i.e., are not capable of chelation) are known inthe art. "Chelating agents" (materials capable of chelation) refers tomaterials which have two or more atoms which may serve aselectronegative donors positioned so that the donor atoms may react witha metal atom, metal ion, or metal surface to form a five-membered orsix-membered ring structure. Donor atoms are selected from oxygen,nitrogen and sulfur. Donor groups include alcohols, enols, phenols,ethers, carboxylic acids and carbonyl groups such as aldehydes, ketones,carboxylic esters and carboxamides, and their thio-analogs.Nitrogen-containing donor groups include imines and amines and moietiesin which the nitrogen atom forms part of a heterocyclic ring. Suchmaterials with two or more donor groups are also known in the art as"bidentate," "polydentate," or "multidentate," and these terms, whenused herein, are used interchangeably.

U.S. Pat. No. 4,612,244 (to Sony Corp.) discloses the potential use of ametal salt of hydroxyacetic acid as a component of a polyurethane binderfor a backside coating of magnetic recording tape. U.S. Pat. No.4,613,545 (to Sony Corp.) discloses the possible use of chloroaceticacid to produce carboxyl-functional magnetic binders. U.S. Pat. No.4,571,364 (to Fuji Photo Film Co.) discloses polyurethane resins formagnetic binders in which lysine (or its salts) or2-alkyl-2-carboxy-1,3-propanediols are incorporated into the polymer.None of these discloses or claims the use of multidentatecarboxyl-functional polyurethanes. U.S. Pat. No. 4,788,103 (to FujiPhoto Film Co.) describes a magnetic pigment binder comprising apolyurethane containing a polar group such as a carboxylic acid or acarboxylic acid salt. Barium ferrite particles are among thosedisclosed, but not claimed, as compatible with the binder resin.

A carboxyl-functional polyurethane resin for magnetic media iscommercially available from Sanyo Chemical Industries under the tradename TI7503. Japanese Patent Applications JP 03 64,310 and JP 03 64,314,both to Sanyo, describe a urethane binder prepared by using, inter alia,dimethylolpropionic acid or its ammonium salt. The binders disclosed inthe two Sanyo applications have only isolated carboxylic acid groups.

U.S. Pat. No. 4,096,127, to Akzona, discloses preparation ofcarboxyl-functional polyurethanes by half-esterification of hydroxygroups pendant from the polyurethane backbone with aliphatic or aromaticdicarboxylic acid anhydrides. Acid anhydrides of the invention have noadditional functionality, and the resultant ester-acids are converted tosalts and used as paper sizing agents. No applications towards magneticmedia are taught.

Hydroxylated polycarboxylic acids of low molecular weight, such ascitric acid, tartaric acid or 1-malic acid have been used asnon-chemically-bonded additives in magnetic media articles. U.S. Pat.No. 4,693,930, to 3M, discloses the use of citric acid as alubricant-adsorption inhibitor. Similarly, U.S. Pat. No. 5,066,539, toSony Corporation, discloses the use of citric acid and nitrilotriaceticacid as non-reactive additives to magnetic media preparations.

Chelating agents which are included in polymer systems are alsodescribed in U.S. Pat. No. 5,026,860, assigned to the assignee of thepresent invention, which is incorporated by reference herein.Ethylenically-unsaturated copolymerizable chelating monomers aredescribed. Non-copolymerizable anhydrides are not described.

Blends of polyurethanes with vinyl chloride resins are known in themagnetic pigment binder patent art. Vinyl chloride resins containingpolar functionality, especially sulfonate or ammonium salts, are capableof producing good dispersions by themselves, but these resins generallylack sufficient toughness and flexibility for most product applications.Blending of these vinyl chloride resins with polyurethane resinsimproves toughness of the resulting binder but care must be taken topreserve dispersion quality. Commercially available carboxyl-functionalpolyurethanes are compatible with ammonium vinyl chloride resins but theknown carboxyl-functional polyurethanes interact weakly with pigmentsand produce relatively poor dispersions by themselves and, in general,they degrade the dispersing capability of ammonium vinyl chloride resinswhen blended therewith.

A need thus exists for a polyurethane binder composition which iscapable of irreversible binding of pigment particles and which producessmooth, high loading barium ferrite dispersions which provide pigmentcoatings with low void volume and excellent magnetic and mechanicalproperties, and which are compatible with, e.g., ammonium vinyl chlorideresins.

SUMMARY OF THE INVENTION

We have discovered such a polyurethane binder, magnetic media producedtherefrom, blends of the polyurethane with vinyl chloride resins, andmagnetic media produced therefrom.

Magnetic binders of this invention comprise polyurethane polymers havingpendant carboxylic acid groups prepared by the esterification reactionof a cyclic dicarboxylic acid anhydride moiety containing, at least one,typically 1 to 2, preferably 1 additional polar group(s) in addition tothe two polar --COOH groups contained therein, such as those selectedfrom the group consisting of --OH, --SH, --SO₃ H, and --COOH, with ahydroxyl group directly attached to the polyurethane backbone. Specificexamples of the cyclic dicarboxylic acid anhydride moieties include butare not limited to those selected from the group consisting of cyclicanhydrides of acids selected from the group consisting of citric acid,mercaptosuccinic acid, dimercaptosuccinic acid, nitrilotriacetic acid,sulfosuccinic acid, derivatives thereof, and mixtures thereof. Theseanhydrides may be generated in situ by reaction of the correspondingdicarboxylic acid with isocyanate present in the polyurethane reactionmixture. Blends of the resulting polyurethanes with vinyl chlorideresins such as ammonium vinyl chloride afford superior dispersions andcoatings of magnetic pigments, especially heretofore difficult pigmentssuch as barium ferrite. Without wishing to be bound by theory, wespeculate that the superior dispersions and coatings are a result ofirreversible adsorption of the pigment by the polyurethane of thepresent invention (chelation), leading to a stable adsorbed layer and avery strong pigment-polymer bond.

One aspect of the invention relates to a novel carboxylic acidfunctional polyurethane polymer comprising the reaction product of:

(a) one or more polyisocyanates;

(b) one or more polyols;

(c) one or more compounds selected from the group consisting of cyclicdicarboxylic acid anhydrides, bearing at least one additional polargroup in addition to its polar anhydride group; dicarboxylic acidsbearing at least one additional polar group, in addition to its twopolar carboxyl groups, which dicarboxylic acids are capable of formingcyclic anhydrides; and mixtures thereof.

For magnetic media purposes, the ratio of polyisocyanate to polyol istypically such that the resulting polyurethane is soluble in solvents(i.e., not crosslinked or gelled) and contains excess hydroxylfunctionality (i.e., all isocyanate groups are reacted--the ratio of--NCO groups to --OH groups is less than about 1:1).

Another aspect of the invention relates to a novel curable bindercomposition comprising:

a blend of:

(a) a vinyl chloride copolymer resin; and

(b) the carboxylic acid functional polyurethane polymer described above.

Another aspect of the invention relates to a dispersion comprising:

(a) the carboxylic acid functional polyurethane polymer as describedabove; and

(b) a magnetic pigment dispersed in the polymer.

Another aspect of the invention relates to the above dispersion whichfurther comprises a vinyl chloride resin.

Another aspect of the invention relates to a composite for magneticrecording comprising:

(a) a substrate having a front side and a back side;

(b) a dispersion coating on at least one side comprising the carboxylicacid functional polyurethane polymer as described above; and

(c) a magnetizable pigment and optionally a nonmagnetizable pigmentdispersed in the dispersion on at least one side.

Another aspect of the invention relates to a magnetic recording mediumhaving a magnetizable layer of pigment particles which are dispersed ina binder, wherein the binder comprises a cured composition as describedabove.

Another aspect of the invention relates to a novel method of producingthe carboxylic acid functional polyurethane polymer comprising the stepsof:

(a) forming a reaction product comprising a polyurethane prepolymerhaving a pendant isocyanate group(s) by reacting a molar excess of apolyisocyanate with one or more diols;

(b) forming a cyclic anhydride by reacting a dicarboxylic acid selectedfrom the group consisting of 1,4-dicarboxylic acid bearing at least onepolar group in addition to its two carboxylic acid groups,1,5-dicarboxylic acid bearing at least one polar group in addition toits two carboxylic acid groups, and mixtures thereof with the reactionproduct of step (a) wherein the amount of polar group-containingdicarboxylic acid used is such that the ratio of moles of polargroup-containing dicarboxylic acid to the moles of residual isocyanategroups in the reaction product of step (a) is less than about 0.25 to 1;

(c) forming a hydroxyl functional polyurethane polymer by converting theresidual isocyanate groups of the prepolymer of step (a) which remainunreacted in step (b) to polyurethane via reaction with an excess of apolyol wherein the number of moles of hydroxyl groups contained thereinis greater than the difference between the number of moles of residualisocyanate groups in the prepolymer of step (a) and the number of molesof polar group-containing dicarboxylic acid of step (b) and

(d) allowing the reaction of the cyclic anhydride formed in step (b)with the hydroxyl functional polyurethane polymer thereby esterifyingthe hydroxyl groups with the cyclic anhydride and producing pendantpolar-group functional carboxyl substituents on a polyurethane backbone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the increased adsorption of citric acid-polyurethaneadducts and their blends with E-C130 vinyl chloride-based resin(available from Sekisui) onto magnetic pigment.

FIG. 2 illustrates the increased adsorption of both citricacid-polyurethane and mercaptosuccinic acid-polyurethane adductsrelative to a known unidentate carboxylic acid-polyurethane adductprepared using dimethylolpropionic acid (DMPA).

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises novel carboxyl-functional polyurethanepolymers, magnetic media made therefrom, a method of making thepolyurethane polymers, a blend of the polyurethane polymers with vinylchloride copolymer resins, and magnetic media made from the blends.

I. Method of Preparing Carboxylic Acid Functional Polyurethane Polymers

The general method of preparing the polymers of the present inventioncomprises the reaction of a polar-group functional cyclic anhydride withhydroxyl groups pendant from the backbone of a polyurethane, thepolyurethane being produced from the condensation reaction ofpolyisocyanate(s) with one or more polyols, as defined in Section II,below. The polymer may be prepared in the presence or absence of asolvent. Preferably, the polymerization is carried out in the presenceof an organic solvent selected from the group consisting ofcyclohexanone, toluene, methyl ethyl ketone, tetrahydrofuran, andmixtures thereof. Most preferably, the solvent is selected from thegroup consisting of methyl ethyl ketone and tetrahydrofuran.

A catalyst may be added to promote the reaction, e.g., a tin catalystsuch as dibutyltin dilaurate. The component polyol(s) andpolyisocyanate(s) may be introduced into the reaction mediumindividually in stepwise fashion in order to decrease the random natureof the copolymer. Alternatively, all of the constituent ingredients maybe added to the reaction medium prior to initiating the reaction, in abatch polymerization process, which produces an essentially randomcopolymeric polyurethane. The order of addition of ingredients may havean effect on the viscosity of the resultant polyurethane, and a skilledpractitioner would be able to determine which order will produce adesired viscosity.

We have discovered a surprisingly facile synthesis of polyurethanescontaining multidentate complexing moieties. Reaction mechanisms andrates are such that these polyurethanes can be readily prepared byintroducing the appropriate polar group-containing 1,4-dicarboxylic acidand/or 1,5-dicarboxylic acid into a polyurethane synthesis reactionwhere diisocyanates are undergoing reaction with polyols. The diacid israpidly converted to cyclic anhydride by reaction with some of theisocyanate. If a suitable excess of polyol hydroxyl functionality ispresent, the anhydride and the remaining isocyanate react with availablehydroxyl and the product is a polyurethane containing pendant hydroxylgroups, some or all of which are esterified with the polar groupcontaining diacid. Little or no crosslinking takes place and the productis soluble.

This synthesis succeeds because the reaction of 1,4-dicarboxylic acidsor 1,5-dicarboxylic acids with isocyanates proceeds very rapidly to formcyclic anhydride as the major product. Simple versions of this reactionare known in the literature (see Kirk-Othmer Encyclopedia of ChemicalTechnology, Third Edition, John Wiley, New York, Vol. 13, p. 793,incorporated by reference herein), but we have found that it also occursreadily even when a polar, anhydride reactive group is present in thediacid molecule. This allows us to generate in situ novel anhydrideswhich would be unstable (self-reactive) if isolated in a concentratedform. These anhydrides can then be used to generate novel pendant groupsfrom polyurethanes via reaction with hydroxyl. Infrared spectra wereused to verify the major course and products of the reaction, whereanhydride can be clearly seen to be formed initially and then reacted.It is probable that some of the 1,4-dicarboxylic acid or1,5-dicarboxylic acid reacts with isocyanate by the more usual route toform amide instead of anhyride. This is a slow reaction at thetemperatures involved but it also results ultimately in a polyurethanecontaining pendant polar group with similar multidentate functionality.

Typically, a reaction mixture of one or more diols, dibutyltin dilauratecatalyst, solvent and an excess of a suitable diisocyanate is heated atabout 60° C. to about 80° C. with stirring and allowed to react underanhydrous conditions. Next, the polar-group containing 1,4-dicarboxylicacid or 1,5-dicarboxylic acid or its cyclic anhydride is added andheating continues. Finally, a triol is added, heat is again applied,and, when infrared analysis shows that no isocyanate and no anhydrideremain, the desired carboxyl-functional polyurethane is obtained.

II(a). Polyol

The term "polyol" as used herein refers to polyhydric alcoholscontaining two or more hydroxyl groups and includes diols, triols,tetrols, etc.

II(a)(i). Triols

A preferred class of triols comprises polycaprolactone triols. Oneparticularly useful triol is a polycaprolactone triol having a hydroxyequivalent weight of about 180 and a number average molecular weight ofapproximately 540, available under the trade designation TONE™ 0305 fromUnion Carbide Company. Other useful triols include polycaprolactonetriols other than TONE™ 0305, such as TONE™ 0301 and TONE™ 0310, bothavailable from Union Carbide, polyester triols such as butylene adipatetriols, polyether triols such as the poly(propylene oxide) adduct oftrimethylol propane known as LHT-240™, from Union Carbide, and simpletriols such as trimethylolpropane and glycerol. Tetrafuctional or higheralcohols such as pentaerythritoI may also be useful. Preferably thehydroxy groups in the triol are primary in order to facilitate curing ofthe resultant polymer with a curing agent. It is also foreseen thatmixtures of various triols may be utilized.

II(a)(ii). Diols

A variety of diols may be utilized according to the invention includingboth short chain and long chain diols. Also, mixtures of diols can beused. A preferred class of diols are oligomeric diols defined as diolshaving a hydroxy equivalent weight greater than about 200 (g/eq). Mostpreferred are the polycaprolactone diols and polycarbonate diols havinga hydroxy equivalent weight of from about 200 to 2,000 (g/eq). Suchmaterials include polyester diols such as TONE™ 0210, available fromUnion Carbide Company, having a hydroxy equivalent weight of about 415.Another such material is DURACARB™ 120, a polycarbonate diol from PPGIndustries Inc. having a number average molecular weight of about 900(hexanediol carbonate).

Other useful diols include polyether diols such as polytetramethyleneglycols and polypropylene glycols; and polyester diols, such as apolyester diol that is the reaction product of a mixture of adipic andisophthalic acids and hexane diol. Preferably, at least some lowmolecular weight (less than about 200 number average molecular weight)diols are used to provide preferred hardness characteristics to thepolymer and the magnetic media prepared therefrom. Examples of these areethylene glycol; propylene glycol; 1,3-propane diol; 1,4-butane diol;1,5-pentane diol; 1,6-hexane diol; neopentyl glycol; diethylene glycol;dipropylene glycol; 2,2,4-trimethyl-1,3-pentane diol; cyclohexanedimethanol; 1,4-cyelohexanedimethanol; ethylene oxide and/or propyleneoxide adduct of bisphenol A; and ethylene oxide and/or propylene oxideadduct of hydrogenated bisphenol A. Examples of other diols which may beuseful include macromonomer diols, diols having polar functional groups,diols beating ethylenic unsaturation, such as3-allyloxy-1,2-propanediol, 1-glyceryl (meth)acrylate, 2-glyceryl(meth)acrylate, 2-methylene-1,3-propane diol, pentaerythritoldi(meth)acrylate, trimethylolpropane monoallyl ether,2-acrylamido-2-hydroxyethyl-1,3-propanediol, N,N-diallyltartardiamideand N-allyl-2,2'-iminodiethanol, and fluorinated diols such as C₈ F₁₇SO₂ N[(CH₂)₂ OH]₂. Fluorinated diols can be used in an amount such thatthe fluorinated diol comprises about 0.1 to about 20 weight percent ofthe polymer of the invention. It is further noted that for any of thereactants mentioned, mixtures of materials can be utilized.

II(b). Polyisocyanates

A wide variety of polyisocyanates may be utilized according to thepresent invention. "Polyisocyanates" means any organic compound that hastwo or more reactive isocyanate (i.e., --NCO) groups in a singlemolecule that can be aliphatic, alicyclic, aromatic or a combinationthereof. This definition includes diisocyanates, triisocyanates,tetraisocyantes, etc., and mixtures thereof. Preferably, diisocyanatesare used. Useful diisocyanates include but are not limited to thoseselected from the group consisting of diphenylmethane diisocyanate,isophorone diisocyanate, toluene diisocyanate, hexamethylenediisocyanate, tetramethylxylene diisocyanate, and p-phenylenediisocyanate. It is noted that mixtures of diisocyanates can also beused.

II(c). Hydroxy Groups

For magnetic binder applications, the polymer of the inventionpreferably possesses hydroxy functionality. It is most preferred but notrequired that there be on the average more than about 2 hydroxy groupsper polymer available for crosslinking purposes. Polymers intended formagnetic binder use preferably have a cross-linkable hydroxy groupequivalent weight of from about 500 to about 50,000, most preferablyfrom about 1,000 to about 5,000 (g/eq).

II(d). Polar-Group Substituted Dicarboxylic Acid Anhydrides

Polar-group containing substituted cyclic dicarboxylic acid anhydridesuseful in the invention are represented by formula I ##STR1## whereinR¹, R², R³, and R⁴, are independently selected from the group consistingof --H, --OH, --COOM, --SO₃ M, --SH, --CH₂ COOM, --SCH₂ COOM,--P(═O)(OM)₂, --OP(═O)(OM)₂, and --Y, wherein at least one of R¹, R²,R³, and R⁴ comprises a moiety other than --H or --Y;

Y is selected from the group consisting of linear alkyl groupscomprising from about 1 to about 10 carbon atoms, branched alkyl groupscomprising from about 1 to about 10 carbon atoms, and aryl groupscomprising from about 6 to about 10 carbon atoms;

M is a cation selected from the group consisting of alkali metalcations, H⁺ and ammonium cations;

R¹ and R² together or R³ and R⁴ together can optionally be ═CHCOOH;

X is a divalent moiety independently selected from the group consistingof ##STR2## n represents an integer selected from the group consistingof 0 and 1; R⁵ and R⁶ are independently selected from the groupconsisting of --H, --OH, --COOM, --SO₃ M, --SH, --CH₂ COOM, --SCH₂ COOM,--P(═O)(OM)₂ --OP(═O)(OM)₂, and --Y, wherein M and Y are as definedabove;

R⁷ is a monovalent moiety independently selected from the groupconsisting of --CH₂ COOH, --CH₂ CH₂ COOH, --CH₂ CH₂ N(CH₂ COOH)₂,--(CH₂)₆ N(CH₂ COOH)₂, --(CH₂ CH₂ O)₂ CH₂ CH₂ N(CH₂ COOH)₂, and --CH₂CH₂ N(CH₂ COOH)CH₂ CH₂ OH.

Preferably, R¹, R², R³, R⁴, R⁵, and R⁶ are independently selected fromthe group consisting of --H, --OH, --COOM, --SO₃ M, --SH, --CH₂ COOM,--SCH₂ COOM, and --Y, wherein M and Y are as previously defined.

Preferred polar-group containing substituted cyclic dicarboxylic acidanhydrides useful in the invention include those selected from the groupconsisting of substituted derivatives of 1,4-butanedicarboxylic acidanhydride [formula I(a)] and substituted derivatives of nitrilodiaceticacid anhydride [formula I(b]: ##STR3## and mixtures thereof, wherein forformula I(a) one of the following is true:

(i) R¹ is selected from the group consisting of --OH, --COOH, --SO₃ H,--SH, --CH₂ COOH, --SCH₂ COOH, --CH(COOH)CH₂ COOH, and --CHOHCH₂ COOHand R² ═R³ ═R⁴ ═--H;

(ii) R¹ ═R² ═--SH and R² ═R⁴ ═--H;

(iii) R¹ ═--CH₂ COOH, R² ═ is selected from the group consisting of--CH₃, and --OH, and R³ ═R⁴ ═--H;

(iv) R¹ and R² together comprise ═CHCOOH and R³ ═R⁴ ═--H;

(v) R³ and R⁴ together comprise ═CHCOOH and R¹ ═R² ═--H;

and wherein for formula I(b) the following is true:

R⁵ is selected from the group consisting of --CH₂ COOH, --CH₂ CH₂ COOH,--CH₂ CH₂ N(CH₂ COOH)₂, --(CH₂)₆ N(CH₂ COOH)₂, --(CH₂ CH₂ O)₂ CH₂ CH₂N(CH₂ COOH)₂, and --CH₂ CH₂ N(CH₂ COOH)CH₂ CH₂ OH. The anhydrides offormula I(a) are most preferred according to the present invention.

Preferably, the cyclic dicarboxylic acid anhydride is selected from thegroup consisting of the cyclic anhydrides of acids selected from thegroup consisting of citric acid, mercaptosuccinic acid,dimercaptosuccinic acid, and nitrilotriacetic acid. Most preferably, thecyclic dicarboxylic acid anhydride is selected from the group consistingof citric acid anhydride and mercaptosuccinic acid anhydride.

The cyclic dicarboxylic acid anhydrides of the present invention can bereacted directly or can be generated in situ from their respectivealiphatic dicarboxylic acids. Dicarboxylic acids of the presentinvention are distinguished structurally by the presence of twocarboxylic acid groups within 4 or 5 atoms of each other along theirbackbone. Such dicarboxylic acids are known in the art to form cyclicanhydrides easily under dehydrating conditions, whereby the resultingcyclic anhydride is a five-membered ring or a six-membered ring,respectively. In the dicarboxylic acids herein described, cyclicanhydride formation is the preferred reaction path, as shown in scheme(A), in which citric acid is the polar group functional dicarboxylicacid and RNCO is any available isocyanate moiety. ##STR4##

The cyclic anhydride thus formed reacts with any available hydroxygroups pendant from the polyurethane polymer backbone via anesterification reaction as shown in scheme (B).

Once the cyclic anhydride is formed, it is essentially unreactive towardself-condensation with polar groups present on anhydride molecules inthe reaction mixture, for two reasons. First, these polar groups arerelatively hindered, especially relative to the hydroxyls of thepolyurethane backbone. ##STR5## Second, because of dilution effects,there are relatively few anhydride-based polar groups with which theanhydride can react, again, especially relative to the large number ofpendant hydroxyls on the polyurethane backbone.

Because of the additional requirement that the dicarboxylic acid oranhydride (or both) is substituted with an additional polar group suchas those selected from the group consisting of --OH, --SH, --COOH, and--SO₃ H, the resulting pendant half-ester has, at its terminal ends,both a carboxylic acid group and the additional polar group. Thestructure of the pendant groups, as defined herein, is ideally suitedfor facile complexation with or chelation of metallic species. Thus,metallic materials used as magnetic pigments can readily be bound to thepolyurethane polymer, providing excellent stabilization of the pigmentsand excellent dispersions thereof.

The polymer of the invention preferably has pendant from it at least onegroup of formula II, ##STR6## wherein R¹, R², R³, and R⁴, areindependently selected from the group consisting of --H, --OH, --COOM,--SO₃ M, --SH, --CH₂ COOM, --SCH₂ COOM, --P(═O)(OM)₂, --OP(═O)(OM)₂, and--Y, wherein at least one of R¹, R², R³, and R⁴ comprises a moiety otherthan --H or --Y;

Y is selected from the group consisting of linear alkyl groupscomprising from about 1 to about 10 carbon atoms, branched alkyl groupscomprising from about 1 to about 10 carbon atoms, and aryl groupscomprising from about 6 to about 10 carbon atoms;

M is a cation selected from the group consisting of alkali metalcations, H⁺ and ammonium cations;

R¹ and R² together or R³ and R⁴ together can optionally comprise═CHCOOH;

X is a divalent moiety independently selected from the group consistingof ##STR7## n represents an integer selected from the group consistingof 0 and 1; R⁵ and R⁶ are independently selected from the groupconsisting of --H, --OH, --COOM, --SO₃ M, --SH, --CH₂ COOM, --SCH₂ COOM,--P(═O)(OM)₂ --OP(═O)(OM)₂, and --Y, wherein M and Y are as definedabove; and

R⁷ is a monovalent moiety independently selected from the groupconsisting of --CH₂ COOH, --CH₂ CH₂ COOH, --CH₂ CH₂ N(CH₂ COOH)₂,--(CH₂)₆ N(CH₂ COOH)₂, --(CH₂ CH₂ O)₂ CH₂ CH₂ N(CH₂ COOH)₂, and --CH₂CH₂ N(CH₂ COOH)CH₂ CH₂ OH.

Preferably, R¹, R², R³, R⁴, R⁵, and R⁶ are independently selected fromthe group consisting of --H, --OH, --COOM, --SO₃ M, --SH, --CH₂ COOM,--SCH₂ COOM, and --Y, wherein M and Y are as defined above.

II(e). Pendant Ethylenically-Unsaturated Groups

Optionally, ethylenically-unsaturated groups which are crosslinkablewhen subjected to ionizing radiation may be pendant from thepolyurethane backbone. Such pendant ethylenically-unsaturated groups areproduced by chemical reaction of at least one unsaturated compound whichfurther contains a functional group which is reactive with one or morehydroxyl groups pendant from the polyurethane backbone, as described insection II(c). Useful hydroxyl-reactive functional groups include, forinstance, isocyanate, acid chloride, and anhydride. Usefulfunctional-group containing unsaturated compounds include but are notlimited to those selected from the group consisting of isocyanatoethylmethacrylate, allyl isocyanate, alpha, alpha-dimethyl-m-isopropenylbenzylisocyanate, (meth)acryloyl chloride, itaconic anhydride, toluenediisocyanate-hydroxyalkyl (meth)acrylate adducts, and mixtures thereof.The backbone may have one or more pendant groups, typically a pluralityof pendant groups. Blends of polyurethanes of the invention havingpendant radiation curable methacrylate group(s) with polyurethaneshaving radiation curable allyl moieties are particularly useful.Typically a ratio of about 40:60 to 60:40 is used, preferably about45:55 to 55:45, most preferably about 50:50.

We have found, surprisingly, that magnetic pigments that have heretoforebeen difficult to disperse in magnetic binders known in the art arereadily and thoroughly dispersed in binders comprising the polyurethaneshaving pendant carboxylic acid groups and pendant polar groups of thepresent invention. More particularly, the binders of the presentinvention produce smooth, high loading magnetic pigment dispersionswhich provide coatings having low void volume and excellent magnetic andmechanical properties. The data in FIGS. 1 and 2 support the stronglyabsorbing nature of the pigment-polyurethane interaction described inthe present invention. The pigment-polyurethane interaction appears tobe essentially irreversible.

III. Vinyl Chloride Copolymer

The carboxyl-functional polyurethane polymers of the invention arecompatible with a wide range of vinyl chloride copolymers with whichthey can be optionally blended. The blends can comprise up to about 95percent by weight of a curable hydroxy functional vinyl chloridecopolymer. A curable binder composition blend can be prepared bycombining the carboxylic acid functional polymer of the invention with avinyl chloride copolymer. The blends have a number of advantages,including the following: Such blends afford a good combination ofmechanical properties, particularly hardness and toughness, and superioradsorption onto the surface of magnetic pigments at low polymerconcentrations, that is superior to either polymer alone. Theseproperties are due to the sufficient miscibility of the carboxylic acidfunctional polyurethane polymer of the invention and the vinyl chloridecopolymer. The polymer of the invention provides a strong interface withand adhesion to magnetic pigments which leads to improved wearproperties of the finished coatings. This combination of good mechanicalproperties and excellent irreversible bonding to the pigments is notobtained with polyurethane-vinyl copolymer blends known in the art. Thecurable binder composition of the present invention typically comprisesfrom about 5 percent to about 95 percent by weight of a curable hydroxyfunctional vinyl chloride copolymer, if used, for good balance ofproperties, preferably about 25 to about 75 weight percent for superiorbalance of properties, and most preferably about 45 to about 55 weightpercent for even better balance of properties based upon the totalweight of the curable binder composition. Preferred vinyl chloridecopolymers contain pendant hydroxyl groups to promote solubility, cureand compatibility with other resins. Preferred vinyl chloride copolymersalso contain pendant polar groups to aid in the dispersing of pigments,and optionally, epoxy groups to improve heat stability. Other pendantgroups may optionally be present to impart desired thermal or mechanicalproperties.

The vinyl chloride copolymer can be prepared by various polymerizationmethods, such as emulsion polymerization, solution polymerization,suspension polymerization, and bulk polymerization. In any of suchpolymerization methods, incremental or continuous addition of amolecular weight control agent, a polymerization initiator, and themonomers for copolymerization may be used when necessary. Preferably thevinyl chloride monomer is present in sufficient amount such that thevinyl chloride copolymer has a vinyl chloride monomer content of atleast 60% by weight for reasons of solubility and polymer blendcompatibility.

In order to provide vinyl chloride copolymer having a plurality ofhydroxyl groups pendant from the polymer backbone, monomers containingfree hydroxyl groups are copolymerized into the vinyl chloridecopolymer. These monomers should be present in a sufficient amount suchthat the vinyl chloride copolymer has an hydroxyl equivalent weight ofabout 500 to about 10,000. Examples of suitable monomers having pendanthydroxyl groups include, for example an alkanol ester of anα,β-unsaturated acid such as 2-hydroxylethyl acrylate or methacrylate,hydroxypropyl acrylate or methacrylate, an olefin type alcohol such as3-butene-1-ol, 5-hexene-1-ol, an alkanol vinyl ether such as2-hydroxyethyl vinyl ether, an acrylamide such as N-methlolacrylamide,N-methylolmethacrylamide, and the like. Alternatively, vinyl acetateunits can be copolymerized then partially or fully hydrolyzed to producevinyl alcohol units.

The vinyl chloride copolymer preferably contains monomer units havingpendant epoxy groups in order to retard dehydrochlorination and therebyimprove polymer stability. Examples of suitable monomers include thoseselected from the group consisting of a glycidyl ether of an unsaturatedalcohol such as allyl glycidyl ether, a glycidyl ester such as glycidylacrylate or methacrylate, an epoxidized olefin such as butadienemonoxide, vinylcyclohexene monoxide, and the like. The epoxy monomer maybe used in an amount such that the vinyl chloride copolymer has an epoxyequivalent weight of from about 500 to about 30,000, preferably fromabout 1,000 to about 20,000, for reasons of maximum effectivity.

It is preferable but not essential that the vinyl chloride copolymercontain polar groups to aid in pigment wetting and dispersion. Preferredpolar groups include those selected from the group consisting of --SO,M, --NR₃ X, --NR₂, --OSO₃ M, --COOM, --OPO₃ M, and --PO₃ M where M is acation selected from the group consisting of alkali metal cations (e.g.Na⁺ or K⁺ etc.), H⁺, and ammonium cations, R is selected from the groupconsisting of alkyl comprising 1 to about 30 carbon atoms, aryl, andaralkyl groups, and X is an anion selected from the group consisting ofthe halogens, sulfates, and sulfonates.

The polar groups can be introduced into the vinyl chloride copolymereither through the use of polar initiators, polar monomers, or bypolymer reactions. Whatever method is used, it is desirable that thepolar groups be present in an amount sufficient to provide a vinylchloride copolymer having a polar group equivalent weight of from about2,000 to about 100,000 grams polymer per mole of polar group, preferablyfrom about 5,000 to about 30,000 grams per mole of polar group forreasons of dispersion rheology.

Examples of polar initiators include but are not limited to thoseselected from the group consisting of 4,4'-azobis(4-cyanovaleric acid),succinic acid peroxide, potassium persulfate, and sodium perphosphate.These materials initiate vinyl chloride polymerization and produceterminal carboxyl, sulfate or phosphate groups in the process.

Preferred monomers containing polar groups include those selected fromthe group consisting of acrylic and methacrylic esters and amides,anhydrides, and styrenic monomers. Preferred polar groups are quaternaryammonium, sulfonate, phosphate and carboxyl. Certain combinations ofthese polar monomers are also advantageous, for example quaternaryammonium and phosphate. Methacryloxyethyl trimethyl ammonium chloride,methacryl oxyethyl acid phosphate, acrylamidopropyl sodium sulfonate,sodium styrene sulfonate, acrylic or methacrylic acid, maleic anhydride,and maleic acid are some particularly preferred vinyl comonomers.Examples of useful polar monomers include but are not limited to thoseselected from the group consisting of acrylic acid, methacrylic acid,vinyl sulfonic acid, styrene sulfonic acid,2-acrylamido-2-methyl-1-propanesulfonic acid, dimethylaminoethylmethacrylate, maleic anhydride, phosphate ester of 2-hydroxyethylmethacrylate, methacryloxyethyl trimethylammonium chloride, saltsthereof, and mixtures thereof.

Examples of polymer reactions to produce polar groups are:

(i) reaction of succinic anhydride with hydroxyl groups on a vinylchloride copolymer to produce pendant acid functionality and

(ii) reaction of tertiary amines with epoxy groups on a vinyl chloridecopolymer to produce quaternary amines.

Other types of monomers amenable to copolymerization include thoseselected from the group consisting of various kinds of vinyl esters suchas vinyl acetate, vinylidene chloride, acrylonitrile, methacrylonitrile,styrene, acrylate and methacrylate esters such as methyl acrylate, ethylacrylate, butyl acrylate, and butyl methacrylate and other unsaturatedmonomers such as vinyl ethers, acrylamide, methacrylamide, maleicanhydride, and mixtures thereof.

Some preferred vinyl chloride copolymer resins are described in U.S.Pat. No. 4,816,683, incorporated by reference herein (assigned toSekisui Chemical). These are copolymers of vinyl chloride, hydroxypropylacrylate, methacryloxyethyl trimethylammonium chloride, andmethyacryloxyethyl phosphate. These are thought to be similar to or thesame as the commercially available "S-LEC E-C" resins (E-C130 andE-C110) made by Sekisui Chemical Co. According to information suppliedby the vendor, these are approximately 84% vinyl chloride, 16% hydroxyacrylic monomer by weight) and contain a fraction of a percent of othermonomers, including a quaternary ammonium monomer.

Another preferred class of vinyl chloride copolymers are the sulfonatedvinyl "MR" resins (MR-110, MR-113, MR-120, and others) commerciallyavailable from Nippon Zeon Co. Polymers of this type are described inU.S. Pat. Nos. 4,707,410 and 4,707,411 (assigned to Nippon Zeon), bothincorporated by reference herein. A preferred resin approximatecomposition is as follows: 20,000 sulfonate equivalent weight, 2000hydroxyl equivalent weight, and 5500 epoxy equivalent weight.

Another useful vinyl chloride copolymer is UCARMAG binder 528 from UnionCarbide which contains carboxyl group (about 5600 g/mole) and hydroxylgroups (850 g/mole) and is described in U.S. Pat. No. 4,985,314,incorporated by reference herein.

Vinyl chloride copolymers containing no polar functionality can also beuseful in some cases. An example is VAGH from Union Carbide whichcontains vinyl chloride and hydrolyzed vinyl acetate such that thehydroxyl equivalent weight is about 750 g/mole.

IV. Dispersion of Polymer or Polymer Blend for Use in Magnetic Media

The binder described herein can be used to prepare magnetic media suchas tapes, e.g., video tapes, computer tape and data cartridge tape, anddiskettes, both single-sided and double-sided.

A magnetic or magnetizable pigment can be readily dispersed within thepolymeric binder of the invention, dispersion being facilitated by theincorporated acidic moiety. The preparation of a dispersion of magneticpigment within the polymer or polymer blend of the present invention, isrelatively straight-forward. A variety of pigments may be used,including but not limited to those selected from the group consisting offerric oxides; gamma ferric oxide; cobalt doped gamma ferric oxides;chromium dioxide; iron; iron-cobalt; cobalt; nickel; cobalt-nickel;cobalt-phosphorus; barium ferrite; and mixtures thereof.

It is foreseen that a variety of loadings, densities, solvent systems,adjuvants, etc., may be utilized. The following conditions are typical,and were employed in preparation of some of the dispersions reported inthe examples below (parts by weight unless otherwise noted) about 100parts of pigment such as (Co-γ-Fe₂ O₃) having a surface area 50 m² /gand a powder coercivity of 950 Oersted; about 15 to 40 parts of binder(i.e., polymer or polymer blend); and about 150 to 400 parts of solventare combined with about 750 parts of steel or glass milling media in asteel container and milled by agitation until the pigment is dispersedthroughout.

The coated and dried dispersion of the present invention can be readilycured. Curing is a process in which crosslinking of the binder polymertakes place and which renders the resulting cured polyurethane polymerdimensionally stable and essentially insoluble in common organicsolvents. One method of cure involves use of multi-functional isocyanatecuring agents, the isocyanate groups of which may react with hydroxygroups which may be present on the polymer of the present invention. Acurative is typically added after a dispersion comprising pigment,solvent, and binder is prepared. A typical curative comprises, forexample, a triisocyanate such as the adduct of toluene diisocyanate witha mixture of polyols including, e.g., trimethylol propane. One suchmaterial is available under the trade designation MONDUR™ CB-601 fromMobay Chemical Company. Typical curatives are polyisocyante compounds,for example polyisocyanates such as MONDUR™ CB-601, MONDUR™ CB-75,MONDUR™ MRS (all available from Mobay Chemical Co.), DESMODUR L™(available from Bayer A. G.), and CORONATE L™ (available from NipponPolyurethane). Additional isocyanate curing agents are described in U.S.Pat. No. 4,731,292, incorporated by reference herein. The curative ispreferably added in a proportion of about 1 to 20 weight percent basedupon the binder weight. The binder weight refers to the weight of thepolymer of the invention plus any optional binder such as vinyl chloridecopolymer with which it is blended.

The resulting dispersion can be readily applied to a support such as apolyethylene terephthalate (PET) film using a knife coating method.Examples of supports on which the magnetic coating material can beapplied include but are not limited to those selected from the groupconsisting of polyesters such as polyethylene terephthalate andpolyethylene-2,6-naphthalate; polyolefins such as polyethylene andpolypropylene; derivatives of cellulose such as cellulose triacetate,cellulose acetate butylate, cellulose acetate propionate; polycarbonate;polyvinyl chloride; polyimides; polyamides; metals such as aluminum andcopper; and paper. Immediately after coating and while the solvent isstill present and the binder is substantially uncured, the coatedsubstrate typically is subject to a magnetic field to orient themagnetic particles. After coating and orienting, the substrate is driedof solvent and allowed to cure. The curing retains the pigment in theoriented manner. Curing can take place either at room temperature or atelevated temperatures (50°-60° C.).

Another method of cure involves irradiation of a polymeric bindercontaining radiation-curable moieties such as ethylenically-unsaturatedgroups. Irradiation of the coated and dried dispersion may be achievedusing any type of ionizing radiation, e.g., electron beam radiation orultraviolet radiation, in accordance with practices known in the art.Preferably, curing is achieved with an amount of electron beam radiationin the range of from about 1 to about 20 Mrads, preferably from about 4to about 12 Mrads, and more preferably from about 5 to about 9 Mrads ofelectron beam radiation having an energy level in the range of fromabout 100 to about 400 keV, preferably from about 200 to about 250 keV.Although electron beam irradiation can occur under ambient conditions orin an inert atmosphere, it is preferred to use an inert atmosphere as asafety measure in order to keep ozone levels to a minimum and toincrease the efficiency of curing. "Inert atmosphere" means anatmosphere comprising flue gas, nitrogen, or a noble gas and having anoxygen content of less than 500 parts per million (ppm). A preferredinert atmosphere is a nitrogen atmosphere having an oxygen content ofless than about 75 ppm.

A variety of additives known to those skilled in the art can beincorporated into the dispersion of the present invention. Thedispersion can further comprise additives selected from the groupconsisting of head-cleaning agents, lubricants, dispersants, and wettingagents. It is envisioned that lubricants such as those disclosed in U.S.Pat. Nos. 4,731,292 and 4,784,907, both incorporated by referenceherein, could be added to obtain desired frictional and processingcharacteristics. Examples of useful lubricants include but are notlimited to those selected from the group consisting of C₁₀ to C₂₂ fattyacids, C₁ to C₁₈ alkyl esters of fatty acids, and mixtures thereof.Other examples of useful lubricants include those selected from thegroup consisting of silicone compounds such as silicone oils,fluorochemical lubricants, fluorosilicones, and particulate lubricantssuch as powders of inorganic or plastic materials. Preferred lubricantsinclude those selected from the group consisting of myristic acid,stearic acid, palmitic acid, and butyl and amyl esters thereof.Typically mixtures of lubricants are used, especially mixtures of fattyacids and fatty esters.

If the binder described herein is used as a back-coat for magneticmedia, the back-coat can optionally further comprise non-magnetizablepigments, such as, for example, those selected from the group consistingof carbon black, graphite, aluminum oxide, titanium dioxide, zinc oxide,silica gel, calcium carbonate, barium sulfate, and mixtures thereof.

The dispersion may further comprise an effective amount of a suitabledispersing agent, preferably about 1 to about 10 weight percent basedupon pigment weight in order to disperse the pigment. Suitabledispersants include but are not limited to those selected from the groupconsisting of lethicin and quaternary ammonium acetates or phosphatessuch as EMCOL™ acetate, a polypropylene oxide adduct of diethylethanolamine quarternized with ethylene oxide and acetic anhydride,having a number average molecular weight of about 2300, and EMCOL™phosphate, a polypropylene oxide adduct of diethyl ethanolaminequarternized with ethylene oxide and phosphoric acid. Both are availablefrom Witco Chemical Co. and are disclosed in U.S. Pat. No. 4,837,082incorporated by reference herein.

The dispersion may further comprise about 1 to about 10 weight percentof a wetting agent based upon the weight of the pigment. Suitablewetting agents include but are not limited to those selected from thegroup consisting of phosphoric acid esters such as mono-phosphorylatedpropylene oxide adducts of glycerol, e.g., the reaction product of 1mole of phosphorous oxychloride with the reaction product of 10-11 molesof propylene oxide and 1 mole of glycerine.

Examples of useful head cleaning agents include but are not limited tothose disclosed in U.S. Pat. Nos. 4,784,914 and 4,731,292 bothincorporated by reference herein. Examples of such head cleaning agentsinclude but are not limited to those selected from the group consistingof alumina, chromium dioxide, alpha iron oxide, and titanium dioxideparticles of a size less than about 2 microns which have a Mohs hardnessof greater than about 5 and which are added in an amount ranging fromabout 0.2 to about 20 parts per hundred parts of magnetic pigment.

The detailed description includes exemplary preparations of the polymerblends in accordance with the invention and dispersions preparedtherefrom. All parts, percentages, ratios, etc., throughout theSpecification, including the Examples, are by weight unless otherwiseindicated. In the following examples, the following agents are used:

TONE™ 0210--a polycaprolactone diol produced by Union Carbide, numberaverage molecular weight about 825, hydroxy equivalent weight about 415.

DURACARB™ 124--a polycarbonate diol, number average molecular weightabout 2000, from PPG Industries, Inc.

Neopentyl glycol--a low molecular weight diol, number average molecularweight 104, hydroxy equivalent weight 52, additive for providingpreferred characteristics.

TONE™ 0305--a polycaprolactone triol available from Union Carbide,number average molecular weight about 540, hydroxy equivalent weightabout 180.

Diphenylmethane diisocyanate (MDI)--an isocyanate, number averagemolecular weight 250, isocyanate equivalent weight 125.

MONDUR™ CB-601--a triisocyanate available from Mobay Chemical Company.CB-601 is a toluene diisocyanate-based adduct of unspecified triols anddiols which contains 10.4 percent NCO and is supplied as a 60 percentsolution in ethylene glycol diacetate.

MEK--methyl ethyl ketone

Definition of Terms

Equivalent Weight

The term "equivalent weight" or "Eq. Wt.", as used herein with respectto a functionality or moiety, refers to the mass of polymer per mole, orequivalent, of functionality.

Squareness Ratio

The squareness ratio (Br/Bm), which is the ratio of the remnantsaturation induction, or residual magnetization (Br), to the saturationinduction, or saturation magnetization (Bm), refers to the effectivenessof the orientation of the magnetic particles in a dispersion. Forrandomly-oriented particles, the squareness ratio is 0.5 and for ideallyand perfectly oriented particles, the ratio is equal to 1.0, thus thehigher the value the better.

Inherent Viscosity

The inherent viscosity of each composition was measured to provide acomparison of the molecular weight of each composition. The inherentviscosity was measured by conventional means using a Wescan #50viscometer in a water bath controlled at 25° C. to measure the flow timeof 10 milliliters of a polymer solution (0.5 grams per deciliter ofpolymer in tetrahydrofuran solvent) and the flow time of the solvent. Ineach experiment, inherent viscosity is reported in deciliters per gram.

ICI Viscosity

The ICI viscosity of various magnetic media binder dispersions of theinvention were measured on an ICI Rotating Cone and fixed plateviscometer from Research Equipment, Ltd. (London) which provided ameasurement of viscosity in centipoise.

Smoothness

The smoothness of various magnetic media binder dispersions wasdetermined by microscopic examination and refers to the substantialabsence of any-visible discrete particles. The dispersion uniformity wasjudged qualitatively.

Gloss

"Gloss" refers to the percentage of light incoming at 45° that isreflected at an observation angle of 45° measured via a PacificScientific Glossgard II 45° glossmeter.

Gn

Gn is a dimensionless measure of coercivity distribution given by theexpression:

    Gn=(Hc)/(ΔHc)

where ΔHc is the width of the coercivity range at 1/2 peak height. Gn isthe reciprocal of the switching field distribution.

TEST METHODS

Pigment Adsorption

The degree of adsorption of polymers onto magnetic pigment wasdetermined as follows: 10 grams of magnetic pigment were mixed with 15grams of methyl ethyl ketone and with from 1 to 15 weight percent ofpolymeric binder based upon the weight of pigment in centrifuge-gradetest tubes. The resultant slurries were agitated in an ultrasonic bathfor one hour, then rolled for an additional 24 hours to ensure goodmixing and attainment of equilibrium in the adsorption process. The testtubes were then centrifuged for 45 minutes and the polymer concentrationin the supernatant liquid was analyzed by gravimetric means. The amountof polymer adsorbed on the pigment surface was calculated according tothe following formula:

    Adsorbed amount (i.e., mg polymer/g pigment)=Mo(Ci-Ce)

where

Mo=total amount of polymer plus solvent per unit weight of pigment

Ci=initial polymer weight fraction

Ce=equilibrium polymer weight fraction

Results for adsorption of polymers onto BaFe pigments are presented inFIGS. 1 and 2.

EXAMPLE 1 20,000 Equivalent Weight Citric Acid PolycarbonatePolyurethane

To a 1-liter flask were added 97.9 g DURACARB™ 124 polycarbonate diol(0.098 eq), 25.9 g neopentyl glycol (0.498 eq), 0.1 g dibutyltindilaurate and 381 g MEK. Distillation of 50 g of MEK was followed byaddition of 96.8 g diphenylmethane diisocyanate (0.775 eq). The solutionwas heated to reflux for 1 hour, after which 2.66 g citric acid (0.028eq) were added, after which reflux continued for 1 hour. Then, 54.38 g(0.302 eq) TONE™ 0305 polycaprolactone triol and an additional 82 g MEKwere added and reflux was continued for an additional 2 hours. Infraredspectroscopic analysis showed that all of the anhydride and all of theisocyanate had been consumed. The mixture showed an inherent viscosityof 0.32 dl/g. Citric acid equivalent weight was calculated at 20,000g/eq, and the hydroxyl equivalent weight was calculated to be 1800 g/eq.

EXAMPLE 2 20,000 Equivalent Weight Citric Acid PolycaprolactonePolyurethane

The procedure of Example 1 was followed except that 48.8 g (0.115 eq)TONE™ 0210 polycaprolactone diol, 11.7 g neopentyl glycol, 0.1 gdibutyltin dilaurate, a total of 302 g MEK in charges of 223 g and 79 g,respectively, 57.87 g diphenylmethane diisocyanate (MDI) (0.463 eq), 1.6g citric acid (0.016 eq), 42.73 g TONE™ 0305 polycaprolactone triol, anda final charge of 1.48 g MDI, were used. Final inherent viscosity =0.24dl/g. Calculated citric acid equivalent weight=20,000. Calculatedhydroxyl equivalent weight=1400.

EXAMPLE 3 20,000 Equivalent Weight Mercaptosuccinic Acid Polyurethane

The procedure of Example 1 was followed except that 7.5 kg TONE™ 0210polycaprolactone diol (17.7 eq), 1.9 kg neopentyl glycol (36.7 eq), 10.2g dibutyltin dilaurate, a total of 36 kg MEK in charges of 27 kg and 9kg, 8.9 kg MDI (71.2 eq), 195.8 g mercaptosuccinic acid (1.5 eq), 6.6 kgTONE™ 0305 polycaprolactone triol (36.7 eq), and an additional finalcharge of 590 g MDI (4.72 eq), were used. Final inherent viscosity=0.28dl/g. Calculated mercaptosuccinic acid equivalent weight=19,600.Calculated hydroxyl equivalent weight=1425.

COMPARATIVE EXAMPLE A 20,000 Equivalent Weight Dimethylolpropionic AcidPolyurethane

The procedure of Example 1 was followed except that 48.8 g TONE™ 0210polycaprolactone diol (0.115 eq), 11.7 g neopentyl glycol (0.225 eq),0.1 g dibutyltin dilaurate, a total of 301 g MEK in charges of 222 g and79 g, 57.86 g MDI (0.463 eq), 1.1 g dimethylolpropionic acid (0.016 eq),42.73 g TONE™ 0305 polycaprolactone triol, and a final charge of 1.48 gMDI, were used. Final inherent viscosity=0.26 dl/g. Calculateddimethylolpropionic acid equivalent weight=20,000. Calculated hydroxylequivalent weight=1400.

EXAMPLE 4 Methacrylate-Functional Mercaptosuccinic Acid Polyurethane

To prepare a methacrylate-functional polyurethane, 27.0 g (0.17 g)isocyanatoethyl methacrylate and a few drops of dibutyltin dilauratewere added to 600 g (0.17 eq) of a 43.6% solution of themercaptosuccinic acid polyurethane of Example 3 in MEK in a 1-literbottle. The bottle was sealed and the mixture was heated at 55° C. for16 hours. On cooling to room temperature, infrared spectroscopicanalysis of the reaction mixture showed no residual isocyanate.Calculated methacrylate equivalent weight=1650.

EXAMPLE 5 Allyl-Functional Mercaptosuccinic Acid Polyurethane

To a 2-liter flask were added 214 g TONE™ 0210 polycaprolactone diol(0.503 eq), 30.1 g neopentyl glycol (0.579 eq), 30 g3-allyloxy-1,2-propanediol (0.454 eq; available from Aldrich Co.) and862 g MEK. 75 g MEK were distilled off to dry the mixture. Then, 229.4 gdiphenylmethane diisocyanate (1.835 eq) and 0.2 g dibutyltin dilauratewere added and the mixture was heated at reflux for two hours. Themixture was cooled to 50° C., after which 4.5 g mercaptosuccinic acid(0.03 eq), 86.2 g TONE™ 0305 polycaprolactone triol and 129 g MEK wereadded. The reaction mixture was heated at reflux for one hour, then 3 gdiphenylmethane diisocyanate were added and reflux was continued foranother two hours. Final inherent viscosity=0.30 dl/g. Calculatedhydroxyl equivalent weight=3000. Calculated mercaptosuccinic acidequivalent weight=20,000. Calculated allyloxy equivalent weight=2600.

EXAMPLES 6-9 Preparation of Dispersions

In order to prepare dispersions of magnetic pigment in binders of theinvention, the ingredients as noted were separately introduced into aball mill using steel media and dispersed therein for two hours. Eachresulting dispersion was applied to a 100 micrometers thick polyethyleneterephthalate film using a knife coater and the resulting coated filmswere allowed to stand in a parallel magnetic field of 1800 Gauss forabout one second immediately after coating. On drying, the magneticlayers had thicknesses of about 4-5 micrometers. The viscosity of thedispersions, along with the squareness, 45° gloss, coercivity and outputof the resulting magnetic tapes, are shown in Table I.

EXAMPLE 6

A dispersion of 100 parts barium ferrite pigment, 7.5 parts E-C130 vinylchloride copolymer binder (available from Sekisui), 2 parts myristicacid, 1 part butyl stearate, 3 parts polyisocyanate (MONDUR™ CB-601,available from Mobay), and 7.5 parts of the citric acid polymer fromExample 1 was prepared in 109 parts methyl ethyl ketone, 54 partscyclohexanone and 18 parts toluene.

EXAMPLE 7

The procedure of Example 6 was followed except that the mercaptosuccinicacid polymer of Example 3 was substituted for the citric acid polymer ofExample 1.

COMPARATIVE EXAMPLE 8

The procedure of Example 6 was followed except that the dimethylolpropionic acid polymer of Comparative Example A was substituted for thepolymer of Example 1.

EXAMPLE 9

The procedure of Example 7 was followed except that the barium ferritepigment was replaced by a cobalt-modified iron oxide pigment.

                  TABLE I                                                         ______________________________________                                               Br                Coercivity    Viscosity                              Example                                                                              (Gauss) Squareness                                                                              H.sub.c (Oe)                                                                         45° Gloss                                                                     10000 sec.sup.-1                       ______________________________________                                        6      1577    0.876     1486   69     43                                     7      1412    0.841     1505   69     25                                     8      1204    0.821     1496   46     25                                     9      1157    0.830     775    N/A*   37                                     ______________________________________                                         *N/A = not available                                                     

As the data in Table I indicate, the dispersions of Examples 6 and 7,prepared with the polyurethane binders of the invention, exhibitimproved electromagnetic properties over the binder of ComparativeExample 8 prepared with a non-chelating polyurethane, as indicated byhigher residual magnetization (Br) and higher squareness values. Thehigher 45° gloss values also indicate a high degree of interactionbetween the polymeric binders and the magnetic pigment, yielding asmoother coating. The binder of Example 9 is also shown to exhibitsatisfactory electromagnetic properties using an iron oxide pigment.

EXAMPLE 10 10,000 Equivalent Weight Citric Acid PolycaprolactonePolyurethane

The procedure of Example 1 was followed except that 51.6 g (0.121 eq)TONE™ 0210 polycaprolactone diol, 10.8 g (0.208 eq) neopentyl glycol,0.1 g dibutyltin dilaurate, 58.8 g (0.470 eq) diphenylmethanediisocyanate, 295 g MEK in charges of 236 and 59 g respectively, 3.1 g(0.016 eq) citric acid, 39.1 g (0.217 eq) TONE™ 0305 polycaprolactonetriol were used. Final inherent viscosity=0.24 dl/g. Calculated citricacid equivalent weight=10,000, Calculated hydroxyl equivalentweight=1500.

EXAMPLE 11 5,000 Equivalent Weight Citric Acid PolycaprolactonePolyurethane

The procedure of Example 1 was followed except that 50.0 g (0.118 eq)TONE™ 0210 polycaprolactone diol, 13.7 g (0.264 eq) neopentyl glycol,0.1 g dibutyltin dilaurate, 66.9 g (0.535 eq) diphenylmethanediisocyanate, 279 g MEK in charges of 196 and 73 g respectively, 5.8 g(0.03 eq) citric acid, 55.6 g (0.31 eq) TONE™ 0305 polycaprolactonetriol were used. Final inherent viscosity=0.24 dl/g. Calculated citricacid equivalent weight=5,000. Calculated hydroxyl equivalentweight=1800.

EXAMPLE 12

Dispersions of 16 g barium ferrite pigment (ST 50125 from Toda Co.,Hiroshima, Japan) and 2.6 g of the polymer or polymer blend indicated inTable II were prepared in a mixture of 7.5 g MEK, 2.5 g toluene and 2.5g cyclohexanone with 250 g steel media in a steel milling container. Thecontainer was shaken on a paint shaker for a total of 2 hours (1 hourshaking, 1 hour cooling, 1 hour shaking, 1 hour cooling) whereupon thecontainers were opened and 9.8 g MEK, 3.3 g toluene, 3.3 g cyclohexanoneand 0.8 g aluminum oxide head cleaning agent were added. After 15 minuteadditional shaking, the samples were cooled and coated to a thickness ofabout 3 mils. The gloss and magnetic performance results of each coatingis shown in Table II. A gloss value greater than 30 and a value of Gngreater than about 2.0 is considered good for this pigment and highervalues are better. This indicates that the polymers of the presentinvention are effective in dispersing pigment, and that the blends ofthe current invention show a surprising synergistic effect--blends wereoften more effective than either component used alone.

                  TABLE II                                                        ______________________________________                                        Polymer     Citric Equivalent Weight                                                                     45° Gloss                                                                        Gn                                       ______________________________________                                        Example 11  5,000          65        2.26                                     E-C130/Ex. 11 50/50                                                                       5,000          49        3.32                                     E-C130/Ex. 10 50/50                                                                       10,000         48        2.95                                     Example 10  10,000         39        2.04                                     E-C130                     33        2.75                                     E-C130/Ex. 2 50/50                                                                        20,000         31        2.48                                     Example 2   20,000         14        1.79                                     ______________________________________                                    

EXAMPLE 13 Nitrilotriacetic Anhydride

20 g nitrilotriacetic acid (0.1.5 eq) was combined with 32.4 g aceticanhydride (0.317 eq) in 36 g dimethylacetamide solvent. The reaction washeated for 3 hours whereupon a clear amber solution was obtained.Volatiles were vacuum distilled leaving about 30 g of brown liquid whichwas diluted with 100 g MEK. The small amount of insolubles present werefiltered and discarded. Most of the MEK was removed from the filtrateusing a rotary evaporator leaving 22.2 g of a brown viscous liquid whoseinfrared spectrum was consistent with nitrilotriacetic anhydride.

EXAMPLE 14 10,000 Equivalent Weight Nitrilotriacetic AnhydridePolycaprolactone Polyurethane

To a 1-liter flask were added 51.6 g (0.121 eq) TONE™ 0210polycaprolactone diol, 10.8 g (0.208 eq) neopentyl glycol, 0.1 gdibutyltin dilaurate, and 182 g MEK. 56.1 g (0.45 eq) diphenylmethanediisocyanate was added and the mixture was heated for 1 hour at 75° C.37.3 g (0.21 eq) TONE™ 0305 polycaprolactone triol was added followed by2.8 g nitrilotriacetic anhydride of Example 13 and 56 g MEK. The mixturewas held 3 hours at 75° C. whereupon the anhydride peaks at 1773 and1824^(cm-1) in the infrared spectrum had disappeared. Calculatednitrilotriacetic acid equivalent weight=10,000. Calculated hydroxylequivalent weight=1850.

EXAMPLE 15 Dispersions Made from 10,000 Equivalent WeightNitrilotriacetic Acid Polyurethane

A. A dispersion of 48 g barium ferrite pigment (S 50100 from Toda Co.,Hiroshima, Japan) and 8.4 g of the polymer of Example 14 was prepared ina total of 84 g MEK and coated on a PET film following the procedure ofExamples 6-9. Squareness and gloss results are shown in Table III.

B. A second dispersion containing 4.2 g of the polymer of Example 14 and4.2 g E-C130 polymer was also prepared and coated on a PET filmfollowing the procedure of Example 15B. Squareness and gloss results areshown in Table III.

                  TABLE III                                                       ______________________________________                                        Binder             Squareness                                                                              Gloss                                            ______________________________________                                        Example 14         0.67      4                                                Example 14/E-C130 50/50                                                                          .80       53                                               ______________________________________                                    

In the case of this difficult to disperse pigment, barium ferrite, thepolyurethane of Example 14 was able to disperse the particles butflocculation occurred. The combination of the polyurethane of Example 14with the vinyl chloride copolymer prevented flocculation and produced agood dispersion.

EXAMPLE 16 20,000 Equivalent Weight Malic Acid PolycaprolactonePolyurethane

The procedure of Example 1 was followed except that 55.9 g (0.132 eq)TONE™ 0210 polycaprolactone diol, 11.7 g (0.225 eq) neopentyl glycol,0.1 g dibutyltin dilaurate, 59.3 g (0.475 eq) diphenylmethanediisocyanate, 251 g MEK in charges of 192 and 59 g respectively, 1.1 g(0.008 eq) malic acid, 39.4 g (0.219 eq) TONE™ 0305 polycaprolactonetriol were used. Final inherent viscosity=0.26 dl/g. Calculated malicacid equivalent weight=20,000. Calculated hydroxyl equivalentweight=1800.

EXAMPLE 17 20,000 Equivalent Weight Tartaric Acid PolycaprolactonePolyurethane

The procedure of Example 1 was followed except that 55.9 g (0.132 eq)TONE™ 0210 polycaprolactone diol, 11.7 g (0.225 eq) neopentyl glycol,0.1 g dibutyltin dilaurate, 59.3 g (0.475 eq) diphenylmethanediisocyanate, 251 g MEK in charges of 192 and 59 g respectively, 1.3 g(0.008 eq) D,L-tartaric acid, 39.4 g (0.219 eq) TONE™ 0305polycaprolactone triol were used. Final inherent viscosity=0.29 dl/g.Calculated tartaric acid equivalent weight=20,000. Calculated hydroxylequivalent weight=1800.

EXAMPLE 18 20,000 Equivalent Weight Dimercaptosuccinic AcidPolycaprolactone Polyurethane

The procedure of Example 1 was followed except that 56.5 g (0.138 eq)TONE™ 0210 polycaprolactone diol, 12.2 g (0.235 eq) neopentyl glycol,0.1 g dibutyltin dilaurate, 62.0 g (0.496 eq) diphenylmethanediisocyanate, 264 g MEK in charges of 202 and 62 g respectively, 1.6 g(0.009 eq) 2,3-dimercaptosuccinic acid, 41.2 g (0.229 eq) TONE™ 0305polycaprolactone triol were used. Final inherent viscosity=0.26 dl/g.Calculated dimercaptosuccinic acid equivalent weight=20,000. Calculatedhydroxyl equivalent weight=1500.

EXAMPLES 19-21 Preparation of Dispersions

The following ingredients were separately introduced into a 0.5 literstainless steel milling container and mixed and dispersed therein, for 5hours at 1500 RPMS in order to form a dispersion: 81 g of iron oxidepigment ISk 9966 (available from Ishihara Sangyo Kaisha, Ltd., Tokyo),192 g of methyl ethyl ketone, 600 g of steel media (1.3 mm diameter),and 27 g of the polymer of the invention.

The resulting dispersions were applied to films of a polyethyleneterephthalate (thickness: 25 micrometers) by means of knife coating andthe resulting coated films were allowed to stand in a parallel magneticfield of 1400 Oersted for about one second. The magnetic layers obtainedhad thicknesses of about 5 micrometers. The dispersions for preparingthe tapes of the foregoing examples were evaluated for viscosity. Thesquareness ratio and gloss of the magnetic coatings of the tapesprepared in the foregoing examples were also measured. Smoothness(examined under a microscope) and dispersion viscosity, and squarenessdata is shown in Table IV.

                  TABLE IV                                                        ______________________________________                                                                  Brookfield Viscosity                                Ex.  Binder  Dispersion Quality                                                                         cps        Squareness                               ______________________________________                                        19   Ex. 16  Smooth       15000 at 52% solids                                                                      .77                                      20   Ex. 17  Smooth        3750 at 36% solids                                                                      .69                                      21   Ex. 18  Smooth        1840 at 36% solids                                                                      .75                                      ______________________________________                                    

The data in Table IV indicate that binders 16, 17, and 18 can providedispersions which are smooth and can be oriented.

While this invention has been described in connection with specificembodiments, it should be understood that it is capable of furthermodification. The claims herein are intended to cover those variationswhich one skilled in the art would recognize as the chemical equivalentof what has been described herein.

What is claimed:
 1. A dispersion for use in magnetic recording mediacomprising:(a) a carboxylic acid functional polyurethane polymercomprising the reaction product of:(i) one or more polyisocyanates; (ii)one or more polyols; (iii) one or more compounds selected from the groupconsisting of cyclic dicarboxylic acid anhydrides bearing at least oneadditional polar group in addition to its polar anhydride group;dicarboxylic acid(s) beating at least one additional polar group inaddition to its two polar carboxyl groups which are capable of formingcyclic anhydrides; and mixtures thereof; and (b) a magnetizable pigmentdispersed in said polymer.
 2. The dispersion of claim 1 which furthercomprises an additive selected from the group consisting ofnonmagnetizable pigments, lubricants, dispersants, wetting agents, andcuratives.
 3. The dispersion of claim 1 wherein said pigment is selectedfrom the group consisting of ferric oxides; gamma ferric oxide; cobaltdoped gamma ferric oxides, chromium dioxide, iron, iron-cobalt, cobalt,nickel, cobalt-nickel, cobalt phosphorous, barium ferrite, and mixturesthereof.
 4. The dispersion of claim 1 wherein said dispersion furthercomprises nonmagnetizable pigment selected from the group consisting ofcarbon black, graphite, aluminum oxide, titanium dioxide, zinc oxide,silica gel, calcium carbonate, barium sulfate, and mixtures thereof. 5.A composite for magnetic recording comprising:(a) a substrate having afrom side and a back side; (b) a dispersion coating on at least one sideof said substrate comprising a carboxylic acid functional polyurethanepolymer comprising the reaction product of:(i) one or morepolyisocyanates; (ii) one or more polyols; (iii) one or more compoundsselected from the group consisting of cyclic dicarboxylic acidanhydrides bearing at least one additional polar group in addition toits polar anhydride group; dicarboxylic acid(s) bearing at least oneadditional polar group in addition to its two polar carboxyl groupswhich are capable of forming cyclic anhydrides; and mixtures thereof;and (c) a magnetizable pigment and optionally a nonmagnetizable pigmentdispersed in said dispersion on at least one side of said substrate. 6.A magnetic recording media having a magnetizable layer of pigmentparticles which are dispersed in a binder wherein said binder comprisesthe a carboxylic acid functional polyurethane polymer comprising thereaction product of:(i) one or more polyisocyanates; (ii) one or morepolyols; (iii) one or more compounds selected from the group consistingof cyclic dicarboxylic acid anhydrides bearing at least one additionalpolar group in addition to its polar anhydride group; dicarboxylicacid(s) beating at least one additional polar group in addition to itstwo polar carboxyl groups which are capable of forming cyclicanhydrides; and mixtures thereof.
 7. The composite of claim 5 whichfurther comprises an additive selected from the group consisting ofnon-magnetizable pigments, lubricants selected from the group consistingof fatty acids, fatty acid esters and fluorochemical lubricants,dispersants, wetting agents, and curatives.
 8. A compositioncomprising:(a) about 5 to 95 weight percent of a vinyl chloridecopolymer; and (b) about 5 to about 95 weight percent of a polymerselected from the group consisting of a carboxylic acid-functionalpolyurethane polymer comprising:a plurality of --COOH groups pendantfrom a polyurethane polymer backbone, wherein the polyurethane polymerhas an --COOH equivalent weight of from about 1000 to about 100,000;wherein said carboxylic acid-functional polyurethane polymer is obtainedby the condensation reaction of at least one hydroxyl group pendant fromsaid polyurethane polymer backbone with an aliphatic polar-groupsubstituted dicarboxylic acid anhydride selected from the groupconsisting of anhydrides represented by formula I, ##STR8## wherein R¹,R², R³, and R⁴, are independently selected from the group consisting of--H, --OH, --COOM, --SO₃ M, --SH, --CH₂ COOM, --SCH₂ COOM, --P(═O)(OM)₂,--OP(═O)(OM)₂, and --Y, wherein at least one of R¹, R², R³, and R⁴comprises a moiety other than --H or --Y; Y is selected from the groupconsisting of linear alkyl groups comprising from about 1 to about 10carbon atoms, branched alkyl groups comprising from about 1 to about 10carbon atoms, and aryl groups comprising from about 6 to about 10 carbonatoms; M is a cation selected from the group consisting of alkali metalcations, H⁺ and ammonium cations; R¹ and R² together or R³ and R⁴together can optionally be ═CHCOOH; X is a divalent moiety independentlyselected from the group consisting of ##STR9## n represents an integerselected from the group consisting of 0 and 1; R⁵ and R⁶ areindependently selected from the group consisting of --H, --OH, --COOM,--SO₃ M, --SH, --CH₂ COOM, --SCH₂ COOM, --P(═O)(OM)₂ --OP(═O)(OM)₂, and--Y, wherein M and Y are as defined above; and R⁷ is a monovalent moietyindependently selected from the group consisting of --CH₂ COOH, --CH₂CH₂ COOH, --CH₂ CH₂ N(CH₂ COOH)₂, --(CH₂)₆ N(CH₂ COOH)₂, --(CH₂ CH₂ O)₂CH₂ CH₂ N(CH₂ COOH)₂, and --CH₂ CH₂ N(CH₂ COOH) CH₂ CH₂ OH.
 9. Thecomposition of claim 8 wherein the --COOH group equivalent weight of thepolymer of element (a) ranges from about 2000 to about 30,000; and thehydroxy equivalent weight of the polymer of element (b) ranges fromabout 1,000 to about 10,000.
 10. The composition of claim 8 wherein saidvinyl chloride copolymer has incorporated therein at least one pendantpolar group selected from the group consisting of --SO₃ M, --NR₃ X,--NR₂, --OSO₃ M, --COOM, --OPO₃ M, and --PO₃ M, wherein M is a cationselected from the group consisting of alkali metal cations, H⁺ andammonium cations, wherein R is selected from the group consisting ofalkyl groups comprising about 1 to about 20 carbon atoms, and aralkylgroups comprising about 1 to about 20 carbon atoms, and wherein X is ananion selected from the group consisting of halogens, sulfates, andsulfonates.
 11. The composition of claim 10 wherein M is selected fromthe group consisting of Li⁺, Na⁺, K⁺, H⁺, NR₄ ⁺ and mixtures thereof.12. The composition of claim 8 wherein said vinyl chloride copolymer hasincorporated therein epoxy group(s), said vinyl chloride copolymerhaving an epoxy equivalent weight of from about 500 to about 30,000, ahydroxy equivalent weight of about 500 to about 5000, and a sulfonateequivalent weight of from about 5000 to about 100,000.
 13. Thecomposition of claim 8 wherein said vinyl chloride copolymer hasincorporated into its structure a monomer selected from the groupconsisting of vinyl acetate, vinyl alcohol, hydroxypropyl acrylate,hydroxypropyl methacrylate, hydroxyethyl acrylate, and hydroxyethylmethacrylate.
 14. The composition of claim 8 wherein said polyurethanepolymer further comprises one or more pendant radiation-curablemoieties.
 15. The polyurethane polymer of claim 14 wherein the radiationcurable moieties are (meth)acrylate moieties.
 16. The polyurethanepolymer of claim 14 wherein the radiation curable moieties are allylmoieties.
 17. A dispersion for use in magnetic recording mediacomprising:(a) the composition of claim 8; and (b) a magnetizablepigment dispersed in said composition.
 18. The dispersion of claim 17which further comprises an additive selected from the group consistingof nonmagnetizable pigments, lubricants, dispersants, wetting agents,and curatives.
 19. The dispersion of claim 17 wherein said pigment isselected from the group consisting of ferric oxides; gamma ferric oxide;cobalt doped gamma ferric oxides, chromium oxide, iron, iron-cobalt,cobalt, nickel, cobalt-nickel, cobalt phosphorous, barium ferrite, andmixtures thereof.
 20. The dispersion of claim 17 wherein said dispersionfurther comprises nonmagnetizable pigment selected from the groupconsisting of carbon black, graphite, aluminum oxide, titanium dioxide,zinc oxide; silica gel, calcium carbonate, barium sulfate, and mixturesthereof.
 21. A composite for magnetic recording comprising:(a) asubstrate having a front side and a back side; (b) a dispersion coatingon at least one side of said substrate comprising the composition ofclaim 8; and (c) a magnetizable pigment and optionally a nonmagnetizablepigment dispersed in said dispersion on at least one side of saidsubstrate.
 22. A magnetic recording medium having a magnetizable layerof pigment particles which are dispersed in a binder wherein said bindercomprises the composition of claim
 8. 23. A magnetic recording mediahaving a back-coat comprising the cured composition of claim 8.